Multi-mode helix antenna



Dec. 31, 1968 I J. AAsTED 3,419,875

MULTI-MODE HELIX ANTENNA Filed Aug. 8. 1966 DIRECT DEMODULATING CIRCUITRY TRANSMITTER RECEIVER CIRCUITRY INVENTOR.

l JORGEN AASTEDv ,BY Iam-@M m United States Patent C 3,419,875 MULTI-MODE HELIX ANTENNA .lorgen Aasted, San Diego, Calif., assignox' to Ryan IAeronautical Company, San Diego, Calif. Filed Aug. 8, 1966, Ser. No. 571,075 11 Claims. (343-895) This invention relates -to a helix antenna and more particularly to a helix antenna that may be used as a mono-pulse transmitting and receiving antenna in tracking systems.

Antennas used for transmitting and receiving in tracking systems generally have radiation patterns that allow sensing of the return tracking signal. The sensing of the antenna is generated as a diiference in the amplitude of the electric field received or of the phase of the electric field received or of both. Normally, two orthogonal channels are used so that the antenna can track in two dimensions. Antennas for such use are known as mono-pulse antennas and can take the form of parabolic dishes with a feed horn cluster or four helical antennas, or four yagi antennas arranged on the corners of a square. All of these antennas are large and awkward to use. However, it is very desirable to have a mono-pulse antenna that is small and compact in size, has a unitary, simple and relatively inexpensive construction and that is light Weight.

It is therefore an object of this invention to provide a novel and improved antenna.

It is another object of this invention to provide a new and improved helix antenna.

It is another object of this invention to provide a new and improved mono-pulse antenna.

It is another object of this invention to provide a new and improved helix antenna that has directional radiation and receiving capabilities.

It is another object of this invention to provide a novel and improved helix antenna that is capable of generating an improved narrow beam of higher modes.

It is another object of this invention to provide a new and improved helix antenna that provides mono-pulse antenna capability by using multi-mode excitation.

It is another object of this invention to provide a new and improved helix antenna that is capable of separating the information channels so that in two channels, directional error information is detected with narrow band capability for null tracking and in a separate channel the modulated signal is detected with wide band capability for wide band demodulation of the modulating signal.

It is another object of this invention to provide a new and improved helix antenna that can be excited throughout its length.

It is another object of this invention to provide a new and improved antenna that is capable of providing monopulse operation with a single, simple, and inexpensive unitary antenna construction.

The foregoing objects of this invention are provided by a self tracking helical antenna system having a helical shaped conductor member with a stripline circuit means comprising a plurality of strip members arranged in the inner volume of the helix for selectively feeding high frequency energy to the helical shaped conductor along its entire length. A ground plane member is positioned within the volume dened by the helix and the strip members. A disc member supports the antenna structure. The outer helix is supported by insulating members that are in turn fixed to the strip members that are secured to the disc member. The ground plane is also secured to the disc member at substantially the longitudinal axis of the helix and within the strips and may take the form of two intersecting metal plates or a metallic cylinder. Excitation for F 3,419,875 Patented Dec. 31, 196s the antenna is supplied by co-axial cables that pass through the disk to the strip members.

In operation, the stripline members can, depending upon the phase of the supplied signal, provide directional radiation from the antenna in the form of end lire radiation or radiation in higher modes which have maximum radiation in other than the axial direction. Control of the phases of the high frequency signal excitation to the stripline circuit controls the direction of the radiated beam and the modes.

The structural relationship of the striplines, the helical shaped conductor and the ground plane can be used to cause the antenna structure to operate at higher order modes for tracking purposes. Also in the sensing operation, the incoming radiation pattern is detected by the plurality of striplines orthogonally, thereby sensing up or down or right or left of the signal from a tracked transmitter while simultaneously the helical conductor member provides a separate information channel for direct demodulation of the modulated signal received from the transmitter.

Other advantages, the additional objects and features of the invention, will become apparent from the following detailed description which is accompanied by the drawing, in which:

FIGURE 1 is a perspective view of an embodiment of the helix antenna of my invention.

FIGURE 2 is a side view with part removed of an embodiment of the helix antenna of my invention with the transmitter receiver circuitry.

FIGURE 3 is an end view of a modified embodiment of the helix antenna of my invention.

Referring now to FIGURE l, there is shown an embodiment of an end tire, mono-pulse, helix antenna of my invention. The antenna structure is mounted on a disc 14 that may be made of conductive material having suficient strength and rigidity for the purpose. Mounted on disc 14 are four longitudinal strip members or striplines 22 comprising a stripline circuit means. Each of the four striplines 22, which are made of conductive material, are positioned at right angles to the adjacent striplines and are thus located at degree intervals relative to the circumference of the antenna. The striplines each have a longitudinal bar of insulation 16 secured thereon by any suitable fastening means such as cementing or the like. The insulating bars have a plurality of apertures 44 along their length for receiving convolutions of the helical shaped conductor 12. Thus, the strips 20, 21, 22 and 23 structurally support the helical member and provide rigidity to the entire antenna structure.

Positioned in the center of the cylindrical volume encompassed by the helically shaped conductor member 12 and the strip member 22, is a ground plane member 24 that is fixed to disk 14. The ground plane member in the embodiment shown in FIGURE 1 comprises a pair of metal plates joined at right angles. The ground plane member may have other forms such as a cylindrical shape 29 as shown in FIGURE 3.

Each of the strip members 20, 21, 22 and 23 are conductors that are insulated from disc 14 by a suitable layer of insulation 50. The strip members are held to disc 14 by the co-axial connections 30 and 40 that pass through disc 14 and make an electrical connection therethrough. Co-axial connector 38 feeds the helical shaped conductor through aperture 26 in disc 14. The ground plate member 24 is directly secured to disc 14. Known transmitter-receiver circuitry selectively provides high frequency energy through lines 32 and 42, for example, to the individual strip members and through co-axial line 36 to the helical conductor.

Operation.

In transmitting a radiation pattern, the pattern is generally directed along the longitudinal axis of the helical shaped conductor means in a direction away from disc 14. High frequency energy is fed from transmitter receiver circuitry 34 to one or more of the strip conductor members 20, 21, 22 and 23, which in turn excite each convolution of the helical shaped conductor, directly, throughout the length of the helix. This provides substantially uniform excitation of the helical shaped conductor throughout its length and thus improves the generation of a narrower beam.

In prior art helix antennas, there may be several energy exchanges between two modes, the free space mode and a mode where a slow wave propagates on the helix. The helix conductor is normally constructed so that only one mode can exist. Usually this mode comprises the fastest of the slow waves. This results in a -radiation pattern with a maximum in the axial direction or end fire radiation. If the helix diameter is increased, several other modes can then exist and some of these modes will have radiation patterns with maximum of radiation off-set from the axis and a null in the higher modes in the end fire direction. If these modes are excited simultaneously with the basic mode a radiation pattern exists, which may be used for a tracking system. The diameter and pitch of the prior art helix antennas are such that, at a given frequency, higher order modes of slow waves cannot exist.

In my invention the slower wave modes are excited by a stripline circuit that runs the length of the helix, and the diameter and pitch of the helix are chosen such that higher order modes can exist on the helix at the design frequency. The length and other parameters of my helix antenna structure may be so designed that with the coupling between the helix conductor and the strip members, the basic slow wave mode in the helix will take the maximum energy from the free space mode. This permits operation with a maximum of output energy. The combination of the stripline, the helical conductor and the ground plane permit maximum energy coupling with reduced energy losses from leaking out beyond the helix.

Transmission In transmission, high frequency energy such as, for example, 1200 megacycles is supplied by the transmitterreceiver circuitry 34 to the respective strips 20, 21, 22 and 23 through co-axial conductors 32 and 42, 68 and 78. When the phase in each of the signals transmitted to the respective strips is the same, then maximum end fire radiation will result. When the phase of the high frequency energy to the strip-lines differ, then the radiation will be at a given angle from the longitudinal axis of the antenna in an amount determined by the respective phase relationships. For example, if the phase of signal transmitted to striplines 22 and 23 lags the signals transmitted to striplines 20 and 21, then the radiated narrow beam will be inclined at an angle toward striplines 22 and 23. If the signal from striplines 22 and 23 leads the signal transmitted to lines 20 and 2l, then the narrow beam would be angled towards lines 20 and 21. It may be seen that by selectively adjusting the phase of signals to each of the striplines, the stripline circuitry may be used to selectively position the beam in any quadrant. If the upper and lower strips are 180 degrees out of phase then the beam will split giving a higher order mode pattern with front and back lobes as is required for tracking.

It should be recognized that a signal on the helical wound conductor is not necessary for radiation.

Receiving In the receiving or sensing operation, the angle of the incoming signal is determined by the difference in amplitude of the electrical field or its phase as received by the four strip members 20, 21, 22 and 23. The output of these strip members passes through co-axial connectors 32, 42, 68 and 78 to the receiver circuitry 34, where the signal reception means may be used to determine the exact position of the object tracked and provide a change in angle of the transmitted beam from the antenna to keep the tracked object in the null point of the tracking beam. The circuitry may be narrow band to achieve a narrow null point.

Any modulated information on the incoming signal will be received by the helical wound conductor 12 and taken ofi through co-axial line 36 to the direct demodulation circuitry 34 for direct demodulation. Also the incoming demodulated signal may, of course, be received on the strip members and then demodulated in the normal manner of demodulating information in mono-pulse antenna systems. The advantage of using the helical wound conductor 12 as the receiver for the demodulated signal is because the demodulation circuitry can then have a wider band capability. Thus, the normal conflict between narrow band reception for tracking and wide band reception for demodulation is alleviated.

Although one form of the invention has been shown and described by way of illustration, it will be understood that it may take different forms in various other embodiments which come within the scope of the appended claims.

I claim:

1. A mono-pulse helix antenna for transmitting or receiving high frequency radiation patterns comprising,

helically shaped conductor means,

stripline circuit means positioned within the volume of said helically shaped conductor means for selectively feeding or receiving high frequency energy to or from said helically shaped conductor means along the length thereof,

and ground plane means positioned within the volume defined by said stripline circuit means.

2. The mono-pulse helix antenna defined in claim 1 in which said stripline circuit means comprises a plurality of strips of conducting material positioned parallel to the longitudinal axis of and adjacent to said helically shaped conductor means.

3. The mono-pulse helix antenna defined in claim 2 in which said stripline circuit means comprises four strips of conducting material positioned at degree arc points.

4. The mono-pulse helix antenna defined in claim 3 in which said ground plane means comprises a longitudinal member with a diameter slightly less than the diameter of the volume defined by said strips of conducting material.

5. The mono-pulse helix antenna defined in claim 4 in which the ground plane means comprises a. cylinder.

6. The mono-pulse helix antenna defined in claim 4 in which the ground plane means comprises thin intersecting longitudinal conductors.

7. The mono-pulse helix antenna defined in claim 4 in which said helically shaped conductor means and said strips of conducting material and said ground plane means are secured at one end to a plate means.

`8. The mono-pulse helix antenna defined in claim 8 in which said strips of conducting material have insulation means on their outer surface for supporting the length of said helically shaped conductor means.

9. The mono-pulse helix antenna defied in claim 3 having means for individually feeding high frequency energy to each of said strips of conducting material with different selective phase relationships.

10. The mono-pulse helix antenna defined in claim 3 having first circuit means electrically connected to said strips of conductor material for directly translating tracking signal information into object location and,

simultaneously second circuit means electrically connected to said helically shaped conductor means for receiving said tracking signal and directly translating modulated information therein.

11. A helix antenna comprising,

a longitudinal ground plane member,

6 at least two longitudinal strips of conducting material References Cited being spaced from and extending along the longitudi- UNITED STATES PATENTS nal length of sald ground plane member, at least one helically shaped conductor being wound 2,945,227 7/1960 B'roqssaud 343-895 3,144,648 8/1964 Dollmger 343-1895 around said ground plane member and said longitudi- 5 nal strips over a substantial portion of the length of said ground plane member and said longitudinal strips,

and circuit means being connected to said longitudinal US C1' X'R' strips for feeding high frequency energy from said 10 343-830 strips.

ELI LIEBERMAN, Primary Examiner. 

1. A MONO-PULSE HELIX ANTENNA FOR TRANSMITTING OR RECEIVING HIGH FREQUENCY RADIATION PATTERNS COMPRISING HELICALLY SHAPED CONDUCTOR MEANS, STRIPLINE CIRCUIT POSITIONED WITHIN THE VOLUME OF SAID HELICALLY SHAPED CONDUCTOR MEANS FOR SELECTIVELY FEEDING OR RECEIVING HIGH FREQUENCY ENERGY TO OR FROM SAID HELICALLY SHAPED CONDUCTOR MEANS ALONG THE LENGTH THEREOF, 